In industrial control systems, it is often desirable to move objects from one location to another for accomplishing various tasks. For example, rolling conveyors are often used to move objects from one location to another for interacting with different machines of an industrial control process, such as a first machine at a first location for placing a box, a second machine at a second location for filling the box, and a third machine at a third location for closing the box.
More recently, a track system has been developed in which multiple “carts” can be independently driven along a “track” for accomplishing the various tasks of the industrial control process. By providing independently controllable carts, the timing of each task can be more precisely controlled than traditional systems such as rolling conveyors.
In such track systems having moving carts, it is often desirable to know the position of each cart at all times, including during power-up, to ensure that the industrial control process is executing correctly. To accomplish this, each cart can be configured with an encoder scale, such as a magnetic scale, and the track can be configured with arrays of sensors, such as magnetic sensors, with an air gap between the encoder scale and the sensors. In operation, when an encoder scale on a moving cart is near a group of sensors on the track, the sensors can determine the absolute position of the cart by measuring the varying magnetic field strength or varying magnetic field angle from the magnetic encoder scale on the cart. Conversely, when the cart is away from the group of magnetic sensors on the track, the magnetic sensors no longer sense the position magnet of the cart and, in turn, no longer generate output signals having measureable amplitudes. Accordingly, the magnetic sensors can be used to determine absolute positions of carts on the track. It is desirable to improve the aforementioned feedback system.